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Measuring & Mapping

Where, how far, and how much? People have invented an astonishing array of devices to answer seemingly simple questions like these. Measuring and mapping objects in the Museum's collections include the instruments of the famous—Thomas Jefferson's thermometer and a pocket compass used by Meriwether Lewis and William Clark on their expedition across the American West. A timing device was part of the pioneering motion studies of Eadweard Muybridge in the late 1800s. Time measurement is represented in clocks from simple sundials to precise chronometers for mapping, surveying, and finding longitude. Everyday objects tell part of the story, too, from tape measures and electrical meters to more than 300 scales to measure food and drink. Maps of many kinds fill out the collections, from railroad surveys to star charts.

An octant measures angles by bringing two images together—that of the sun, for instance, and the horizon—and was used primarily to determine latitude at sea. The form was described by John Hadley in London in 1731 and still in use in the early twentieth century.

This example is marked "B. CONDY PHILADELPHIA 1778," the signature being that of Benjamin Condy (d. 1798). It was made during the American Revolution, and there are faint markings on the scale that may read "equality" and "justice." It has a mahogany frame and index arm, and ivory inset. The boxwood scale is graduated every 20 minutes from -5° to +95° and read by ivory vernier to single minutes of arc. There is also a back sight and a back horizon mirror for measuring angles greater than 90°. The radius is 17.75 inches.

This is a spectroscope, designed to be used with a telescope to study the light of the sun. It was made in Dublin in 1877 by the famous instrument maker Howard Grubb (1844–1931). It was used with the 9 ½ inch Alvan Clark & Sons refractor in the Observatory of Princeton University.

When the College of New Jersey at Princeton hired the astronomer Charles A. Young in 1877, they also gave him funds to equip the new John C. Green student observatory. One of his first purchases was this instrument. It was custom-made, and Young helped refine the design. (Grubb's company later advertised that this was the first such spectroscope that they had sold.) The most unusual feature of this instrument is the use of a complicated system of multiple prisms to disperse the light and produce a highly detailed view of the solar spectrum.

In use, the spectroscope was mounted at the eyepiece end of the telescope and light from the sun would be directed through it. As the light passed from one prism into the next, it would be increasing dispersed, or spread out. To make the instrument more compact, the beam of light was directed first through the upper portion of the prisms and then back through the bottom part. Depending on how it was configured, the light could thus be passed through either 2, 4, 6 or 8 prisms. A particular area of the solar spectrum could be viewed by turning a small chain that moved each prism by the same amount. Because of the large number of optical surfaces involved, the light loss in this instrument was almost certainly in the 90 percent range. This was an advantage when viewing the Sun, but it reduced the usefulness of this instrument for other purposes, such as measuring the spectra of stars. The success of this instrument in making precise measurements of the solar spectrum (and thus revealing information about the composition of the sun and its atmosphere) led to its wider adoption as an important astronomical tool.

This unsigned sextant belonged to Oberlin College, and may date from the time of the founding of that school in 1833. The frame is brass. The silvered scale is graduated every 15 minutes from -5° to +160° and read by vernier with tangent screw and swinging magnifier to single minutes of arc. One trade card in the box is that of Thomas Hemsley (either father or son) who were in business in London throughout the first half of the 19th century, offering a wide variety of instruments and other items for navigational use.

This sextant has a brass frame. The silvered scale is graduated every 10 minutes from -5° to +145° and read by vernier with tangent screw and swinging magnifier to single minutes of arc. The inscriptions read "Frodsham, Liverpool" and "2602." It came from Vassar College, and may have been used by the professor of astronomy, Maria Mitchell.

This compass has a wooden bowl gimbal mounted in a wooden box. The inscription on the paper card reads "EDM. M. BLUNT. CHART, SELLER, N° 202 WATERSTREET, NEW YORK." The signature is that of Edmund March Blunt (1770-1862), a dealer of nautical supplies who moved from Massachusetts to New York City in 1811 and who retired in the mid-1820s. In the center of the card is an image of a robed figure on land leaning on an anchor and gazing at a ship at sea.

This compass is said to have been on the Niagara on September 10, 1813 when, under the command of Oliver Hazard Perry, American sailors defeated a British squadron in the Battle of Lake Erie.

Matthew Berge (d. 1819) worked for Jesse Ramsden in London, succeeded to the business after Ramsden’s death in 1800, used the Ramsden dividing engine, and numbered his sextants in the sequence begun by Ramsden. This example was made in the early 1800s. It has a "double" brass frame and a silvered scale. The signature on the arc reads "Berge London late Ramsden." The scale is graduated every 15 minutes from -2° to +136° and read by vernier with tangent screw and magnifier.

A label in the box relates the instrument’s history. "SEXTANT owned and used by JOHN C. FREMONT on his trip across the continent to CALIFORNIA. Presented by his Daughter, ELIZABETH B. FREMONT, to HON. CHARLES SILENT and by him to FRANK J. THOMAS. Loaned to and used by WELLS MORRIS on U.S. Destroyer "MUGFORD" in GREAT WAR." The sextant bears the engraving, "Berge London late Ramsden" and "1513".

Ref: A. Stimson, "The Influence of the Royal Observatory at Greenwich upon the Design of 17th and 18th Century Angle-Measuring Instruments at Sea," Vistas in Astronomy 20 (1976): 123-130.

The double-framed brass sextant was patented by Edward Troughton in London in 1788, and the form remained popular throughout the first half of the 19th century. This example belonged to Haverford College in Pennsylvania and may have been acquired when that school was founded in 1833. It has a silvered scale that is graduated every 10 minutes from -5° to +145° and read by vernier with tangent screw and swinging magnifier. The inscription reads "W. & S. Jones Holborn London."

Ref: Edward Troughton, "Framing to be used in the construction of octants, sextants, and quadrants," British patent #1644.

This sextant belonged to Haverford College, and probably dates from the second half of the 19th century. The frame is brass. The silvered scale is graduated every 15 minutes from -5° to +130° and read by vernier with tangent screw and swinging magnifier to single minutes of arc. The arc is engraved "JOHN BRUCE & SON, Liverpool."

This sextant is somewhat unusual in that it has a brass frame, reinforced brass index arm, and ivory (rather than metal) scale. This scale is graduated every 10 minutes from -5° to +125° and read by vernier with tangent screw and swinging magnifier to 20 minutes of arc. The "Spencer Browning & Co., London" inscription on the arc refers to a firm that was in business from 1840 to 1870.

This sextant has a brass frame. The silvered scale is graduated every 10 minutes from -5° to +145° and read by vernier with tangent screw and swinging magnifier to 10 seconds of arc. The "Spencer Browning & Rust LONDON" inscription on the arc refers to a firm that was in business from 1784 to 1840.